Diversity receiving system



5 Sheets-Sheet l Sept. 7, 1948.

M. G. cRosBY DIVERS ITY RECEIVING SYS TE M Filed Jan.- 14. 1944 M. G: vcRosBY 2,448,866 D-IVERSITY RECEIVING SYSTEM sheets-sheet 2 Sept. 7, 1948.

Filed Jan. 14, 194-4.

Sept. 7, 1948. M. G. cRosBY 2,448,865

DIVERSITY RECEIVING SYSTEM Filed Jan. 14, 1944 s sheets-sheet 5 C D 1 .Q E F R T E' A R R A A I ATTORNEY Patented Sept. 7, 1948 DIVERSITYBECEIVINGSYSTEM Murray G. Crosby,l Riverhead; N; YZ', assigner to Radiov Corporationot America, af oorporatinfofi Delaware Y Appucation January 14, 1944, serial' No. 513,263

This invention. relates to. diversity. receiving systems.

Itis. known in the art .to provideaselecting system in a.. diversityreceiver for automatically selecting the best of the available signals appear'- ing in. the. receiving. channels, as. a result of' Whichthe bestloneof the receiving. circuits contributes. substantially all ofthe useful' output; In, certain of. these known diversity receivers which.` employ the best signal selectionV feature, cancellation.ordistortion. can occur in .the common. output. when any two receiving channels contribute. the. same amplitude of signal.. This distortion. is produced` by cancellation' between incomingA signals. received over' two antennas which takes placewhen. there isphaseopposition in. the carriers ,impressed upon .theantennas of'the diversity, receiver.

In the. system ofthe present invention, this' distortion is overcome by utilizingcombinations of the incoming signals. at different phase relations, andlwith the provision of a selecting system which utilizes the combinations. of, signals in. a manner. to` prevent cancellation .between incoming signals. Thus, at certainphase and amplitude relations between incoming signals, theselectingsystemof 'the invention selects the best of Vthese signalcombinations, while atotller phase and-amplitude relations of the incoming signalslthe signals areadditively combinedto producea useful output. In the preferred embodiment. of the present. invention, there vare employed two combinations` ofthe incoming sig? nals.;.na1nelyan inephase and an out-of-phase combination. In another embodiment ofthe invention, there are employed four combinations of incoming signals; .namelyan, iii-phase combination, .an .out-of -phase combination, andd two additionalin-phase and..out.ofphase combinations with ii'xed. 90Iphaseshifts relative to the 'rstv mentioned. two .cQmbinations. .i

By means of .the present inventiomljam also able to obtain. a single alternating current outa put from .the diversityA receiving. system and/rA a detected ,modulation output..

A1 more detailed .description [of the invention follows in.. conjunction with a drawing, .wherein Figs. 1 and 2"'illustrate two embodiments .of iadi-E versity receiver system in accordance with the invention, and Fig. `3' graphically illustrates,` `.by means of vector diagrams, the operationof the systems of"Figs. 1 and 2. i

Fig. 1 shows apreferred embodimentlof the diversity receiving system of the vpresent .ins vention in whichzapluralityot vantennas ispro- 1'5 Claims: (Cl. 2503-520) i .2... vided; each'` of; these arranged to' feed tllek collected'y signal'- energyinto' its own. radioirequency' ampliii'er; The different antennas" are locatecl at geographicallyspaced points where'. thep signal does not fa-d'e similarly;

These antennas'. nii-iytbeA polarized in the' same' plane or in` diierentplanes. The'A radiofrequency voltages from each antennal is selectively amplified in" radio frequency ampliers III` land then passed: on to-'ii'equency converters II in which the" received energy isheterodynedwith energylfrom' a common locall oscillator I3`` topro dii-caan intermediate frequency. signal. This intermediate' frequencyx signal isselectively ampli-- fied. in' intermediate frequency amplifiers- I2. Intermediate `frequency 'output from themrst receiving'jchanneliappears .at A4 while intermediatefrequency outputl from" the second receiving channel appears" at Bi The intermediate frequency outputs at A. and B are supplied totwo pairs yof' electron discharge device circuits C and D`. CircuitCcomprises'a"pail-"of tetrodevacuum tubes 40y and4'| having a` puslifpull input circuit and" a push-pull' output`- circuit. CircuitfDfv comprisesA aN paii'of tetrode vacuunrftubesV MIT-andL 4-3` having-a push-pull inputyand` apush-pushoutput: It should benoted that the anodes of the two tubes ofi .circuiti C lare `conected' to oppositeter-V minals of'a parallel tunedV circuitl 44f comprislng the. primarywinding. of :a transformer I4; while the ano'des ofthe-two tubesI ofcircuitD aredirectly *connected* together' and` tovv the upper'ftereminal; of a parallel tuned circuitv 451A comprising the primary i winding; of a' transformer I 15 The intermediate" frequencyv output of the rst receiver 'channel appearingv at' A' issupplied through' lead 3U toithe controlgrid ofioneitube doof circuitC'fand'iby"'way Vof lea'd 3| i to Ythe grid* of tubev 43`-of"-'circuit`'D`. Thev intermediate frequency output of the secondreceivlng channel appearing-'at B? is applied' to the s control l grid of tube 42 i of 'circuit Dby Way of i lead;v 32* and to the controi grid: of "tube 4I of circuit C byv way ofilead 33. krhe secondary-'windings oftrans-l formers I4 t4and I 'I'i comprlseparts of tuned i cir.- cuits 5.0 and"5"| f'whiclr are `directly connected to gether'sby"means'QfIad'34E Other terminals .of thesetuned circuits'iare jconn'ectedto the anodes of.v diode rectiil'rsf'l .and Ixbymeans of'con nections"52 .andm 53,l respectively.'

A bias' resistor'" shunted' by 'a condenser 145 is connectedbetween" ground .anda-point on lead 34. The; cathodes of diodes'V I5? andl I6 are `ncon` nected to a tuned^circuit`47including the pri'-l mary .of a transformer I8. The secondaryfoi antennas being; respectively f transformer I8 is connected to a frequency modulation or phase modulation receiving system 28. This receiving system may include a limiter, if desired, and a conventional discriminator. The transformers I4, Il and I8 are intermediate frequency band pass transformers which are tuned to pass the intermediate frequency signal with its side bands. A single alternating'current output is obtained from transformer I8, while detected amplitude modulation output is obtained from lead 21, in turn connected to the high potential side of bias resistor 25. yThe detected amplitude modulated output from lead 2l can also be used for automaticivolumefcontrol purposes by connecting this lead back to the radio frequency and intermediate frequency amplifiers in known fashion.

The operation of the system of Fig. 1 is clearlyl apparent from an inspection of Fig. 3 which shows the vector relations of the currents in the two pairs of electron .dischargedevice circuits C and D for eight different relative `phase relations which diifer from each other by 45. The voltage vectors A and B of Fig. 3 represent the intermediate frequency outputs from the two receiving channels I and 2 at the locations labeled A and B in Fig. 1.

When theincoming signals impinging on the antennas of the two receiving channels of Fig. 1 are out-of-phase by 180, the intermediate frequency energies from the two channels at A and Bl will `addto each otherin the output of circuit C and vwill oppose or cancel each other in the output of circuit D. This is shown by the vectoridiagrams of linel I, columns C and D of Fig. 3. The diagram ofl column C corresponds to-circuit C and that of lcolurnnD to circuit D. (Columns E and F are used only in connection with Fig. 2.) v

When the signals are 45 `apart in phase, the vector relations are as shown in line 2 of Fig. 3. It will be noted that the resultant R formed by the in-phase combining circuit C .is larger than present invention and shows the system of Fig. 1 provided with an additional two pairs of tetrode vacuum tube circuits E and F one of whose inputs is coupled a fixed 90 phase shift relative to the intermediate frequency energy at B. Thus the intermediate frequency output of channel I at A is coupled over a pair of leads. 35 to E and F, while the intermediate frequency' energy at B is coupled over a pair of leads 36 to a 90 phase shifter 2D. The output of the 90 phase shifter 20 is coupled to the control grids of the vacuum tubes of the two pairs E and F in lsubstantially the same manner as the outputs of the intermediate frequency amplifiers I2 are coupled to the control grids of the two pairs of tubes of circuits C and D. It Will thus be seen that'the pair of tubes 40', 4I of circuit E, like i those of circuit C, have a push-pull input and a that formed in D. ,This larger voutput predomiv nates over the smaller output when the two outputs are combined in the circuits of rectiers I5 and I6. In these rectifier circuits, the larger signal develops a bias across-the common resistor 25 which biases the diodes in accordance with the stronger signal. This bias is too vhigh to allow the weaker circuit to contribute its .proportionate share of output. Consequently, the detected output appearing across resistor 25 and the combined intermediate-frequencyA output across transformer I8 is predominantly composed of.A the output from circuit C. `This selecting action effected by the rectifier circuits is the well known diversity-.action of rectifiers with a common load resistor.-

.When the signals from the two antennas are 90 apart in phase, thevector relations are as shown in line 3. For thiscase, the resultants are equal in magnitude, butl 90 apart in phase. Circuits lC and D will then contribute equally to the combined output, but since theyare 90 apart in phase there can be no cancellation distortion.

The rest of the diagrams of lines 4, 5, Ii, 1 and 8 are self explanatory since they show conditions similar to those of linesA I, 2 and 3. It will be noted that there is either. the case of one circuit predominating over the other in the rectifier circuits, or there is the case of equal amplitudes with the non-distorting condition of a 90 phase relation. i

Fig. 2 illustrates another embodiment of the push-pull output, while the pair of tubes 42', 43 ofcircuit F, like the tubes of Icircuit D, have a push-pull input and a push-push output. The circuits E and F have output transformers ZI and 22 which are coupled to diode rectifiers 23 and 24 in substantially the same manner as the transformers I4 and I'I are coupled to diode rectiiiers I5 andIS. A lead 28 connects the diode resistor 25 to the junction point of the secondary windings of the transformers 2l and 22 so as i to Amake this bias resistor common to the outputs of Vall four pairs of tubes C, D, E and F. A connection 54 connects together the cathodes of the diodes 23 and 24 and the cathodes of the diodes I5 and` I6. Transformers 2| and 22 are also intermediate frequency band pass vtransformers which. are tuned to pass an intermediate frequency `signal'with its side bands. V,

It will thus be seen that there is obtainable from the two channels of the system of Fig. 2 four 4combinations of incoming signals of different phase relations. These four combinations are an iii-phase combinations and an out-ofphase combination, produced by either circuit C or circuit D, and two additional in-phase and out-of-phase combinations of incoming signals with fixed phase shifts relative to the first mentioned two combinations.

Fig. 3 shows, by` means of voltage vectors A and B representing the intermediate frequency outputs from channels I and 2, the different outputs from the circuits C, D, E and F of Fig. 2 for eight different relative phase relations I to 8, inclusive, which differ from each other by 45. The resultant magnitude of these voltage vectors is represented by the vector R. The voltage vectors for pairs of tubes D and C for the eight different relative phase relations I to 8, inclusive, apply equally to Figs. .1 and 2.

In Fig. 3, line I covers the case where the incoming signals are out-of-phase by It will be seen that the output from circuit C will be additive and produce resultant R while the output from circuit D will be opposed or cancelled to produce no output whatever. Due to the fact that pairs E and F are fed with the same currents as are C and vD but 90 phase shifted in the same direction on only tubes 4 I and 42', the outputs of E and F as represented by the resultants R will be equal to each other but the resultants from the pairs E and F will be less than the resultant from pair C. In view of the fact that the resultant from circuit C is greater than the resultant from any of the other pairs, this resultant predominates and Will produce a negative bias on the resistor 25 because of rectification through rectifier I5, and this negative bias will still further reduce the contribution. from the: .otherY threev-tpaiirsrD; E? and F: fTlriemutput in. transformer i8; or-inzleadg; 2J will thuslfpredominantlycontain the: signal from circuit C. The vectorsfoppcsitelineLofi-Fig; 3

illustrate the-case .Where -the two incoming signals y are out.-of=phase byfv45; `In "this case,y the resultantsA from circuits Cfand are substantially equal and-f predominate and since these resultante. are notvery .much different from each other in phse; both. of them. will*k contribute the. useful; output whichwill produce a. negativebias on` resistor 2.5iv tostillffurther reducexthe. contributions from circuits D and-F: Inasmuch as :the-.phase relation between. the; resultantsV constituting the outputs offcircuits C and iEris notfverymuch diierent from zeroidegreesthere 'will'.beno cancellation distortion eiect in the, outputirom the diversity receiving.` system.

xLine` 3 of Fig. 3-. covers thecasewhen the incoming signals are .90 outf-ofi-phaserelativeto each other. The` outputs oi?v circuits CandfD are substantially equal; The output of; circuit' lill is additive, however, while the output of circuit F iscancelled. Thus; since: the resultant output from circuit Eisfthe V.greatest .off all four, circuits, the-useful outputfrom circuitEwill predominate a-ndfproduce :a negatveibias on; resistor 25 which reduces. the contributions Vfrom the otherv three circuits., (155D: and F; In .thistca-se, Where the incoming lsignals .are .90 out-.of-phase relative to each-other, the;,90 phase shifter 2l)` serves to advance: the 90 phase` shift in4 the receiving system. byan additional 90-so asto make ,the energies additive circuit E;

. Line .4; of Fig. s 3f disclosesfthevoltage vectorsin the case where the phase relations between the carriersf differ from-each other by 135. The re. sultantsA fromV circuitsD and E, shown under columns D and E; are fthe greatest of all four circuits, and theseresultants are very nearly in phase with one another. The two of them combine to produce a use fuloutputwhich has no cancellation, distortion. This useful output produces a negative, bias on resistor 2 5.-;whichfurther .reduces thel contributions ,from the circuits-'Gand It should be noted: that' the. caseiof line 4 :issomewhat-,similar tothe caseof line 2; except: that diflferent` circuits contribute the' useful output. Itfshould .also .be noted that thecaseof line 3 is similar tothevcase of line I, exceptrfortlie fact that the: relative relations betweencircuits C and Dandcireuits -EandF 'are reversed.

Lineci Fig;v 3 shows thevector relations when theincoining signals are in phase. The intermediate `frequencyoutputs will add in circuit D and will cancel in the outputof eircuitfC. :The outputsoicircuits E and-Fe will be; equal toeach other but the resultants therefrom will be less thanqthe resultant from circuit D. In viewof the fact thatthe. resultant from circuit lwill be greater than theresultant from any of the other circuits, this Ipredominant'resultant will produce av negative-bias onresistor-25 because of irectication through diode4 I6. which will still 1 further reitlucethe, contributions from the otherl three circuits; The output intransformer I8 or in -lead EL will. thus predominantly contain the signal from circuit D.

I Linev 6 `of Fig; 3.cove1s.y the casevwhere there isla 45 difference in phaserelation between the incoming signals with respect to the rela-tion of line 5. It wil1benoted from line Sythat. the resultants from circuits D` and F, shown under columns D andE,f aresubstantially equal and-predQYl I lete. and; idefnot Adiffer `from each other, very 6.. much Vfrom.. @zeros-phase:-Ieleiien.. Thus.: both circuitsDiano-Ewihcoritribute theusefuloutput and there will .be enocancellation; distortion4 eiect. This` useful: eutput..will vproduce.4 a negative bias; on resistor. 25.tw1f1-ichyWi-1l; still furtherreduce the contributionsafromgpairs.C;.and- .E,

1 laine 'Lof 3; covers the `case l where the` incoming signalsare zout-.ofephase -relative to the relatipn'shownin-lner-5;. The outputs from circuits Gand; Eearesubstantially equal. Theoutputj from circuit E is'cancelledl While theoutput from circuitt1i-is additive. Thus, sincethe resultants-outputrirom circuitF fis the greatest'ofallrfou-r circuits. in this instance; this useful outpute fromtcircuitgifispredominant andproduces anegativel bias en resistor '25 whichreduces the: contributionsvfrom the otherathree circuits.. Itiwillfbe noted that in-the case of line 1, the 90 phase; shifter vservesto further advance the assumedr-QO? vphase `shift between the incoming signaljs in ,thereceivingsystem so as to makethem additive in circuit F.

Laine i8-:.of'1iig. `3; illustrates. .the vectors when the phase-relation between -the incoming signals is advanced :another 459' relative tothe case of line l; y.'Ilif-,M resultantsfrom circuits CA and E are substantiallyfequal andpredomina-te. These two resultantsdonot differ.- greatly from each other in phase relationandihence both contribute the useful-output. which: produces. ai negative bias onvresistor4 25 to vfurtherfreduce` the contributions from circuits DandE.A There will be no canicellation'\ distortionA in this instance.

--Theapparatus in.box.26; may include a discrimina-tor circuitfoffthe typezdescrlbed in Usseln man .Patent 794,932, or in `Seeley Patent 2,121,103'.vv The limiter .may beof` the type describediin-.Wright et: alrPatent 1,964,375, or in DemarestiPatent 2,0473312.. The receiver systemrnay be ofthe type described in my Patents 2g229l640'1andi2230212for eitherv phase or frequency.m modulation reception. Also, the receiver systems may'employ. circuits as shown in my Patents.f.2,23ll;231. and' 2,230,232.

"Iheflanguageangular velocity detection circuit-t` used in the appendedclaims is deemed to referto. a icincuit capable -of 'detecting either Vphase or! frequency. modulated waves.

What is claimed is:

l; sA. diversity. receiving` Asystem comprising a painof:receivingV channels,.a first signal corn.- biningcircuitlcomprisinga pair of electron discharge.devices having a `push-pull output circuit,..a.s.econd signalfcombining circuit comprisingyapair-.of electromdi-scharge devices having a push-pushrcutput..circuit, connections from one ofisaid receiving .channels to the control electrodesqof onlycnedeviceoffeachof said rst and second. signal combining circuits, connections cuit, a second signal combining circuit comprising a pair of electron discharge devices having a push-push output circuit, connections from one of saidrreceiving channels to the control electrodes of only one device of each'of said first and second signal combining circuits, connections from the other receiving channel to the control electrodes of the other devices of each of said first and second signal combining circuits, a rectifier coupled to the output of said first signal combining circuit, a rectifier coupled to the output of said second signal combining circuit, and a common bias resistor for said two rectifiers so arranged that the strongest sign-al passing through one combining circuit and rectified by its associated rectier produces a negative bias on said resistor to reduce the useful output 'from the other combining circuit, a condenser shunting said common bias resistor, and a connection to the high potentialside of said resistor for deriving detected modulation output from said system.

3. A diversity receiving system comprising a pair of receiving channels, a rst signal combining circuit comprising a pair of electron discharge devices having a push-pull output circuit, a second signal combining circuit comprising a pair of electron discharge devices having a pushpush output circuit, connections from one of said receiving channels to the control electrodes of only one device of each of said rst and second signal combining circuits, connections from the other receiving channel to the control electrodes of the other devices of each of said rst andsecond signal combining circuits,l a rectifier coupled to the output of said rst signal combining circuit, a rectifier" -coupled to the output of said second signal combining cir-- cuit, a direct connection between the cathodes oi said rectiers, an alternating current circuit coupled to said cathodes, and an angular velocity detection circuit coupled to said alternating current circuit, and a common bias resistor for said two rectifiers so arranged that the strongest signal passing through one combining circuit and rectied by its associated rectiier produces a negative bias on said resistor to reduce the useful output from the other combining circuit.

4. A diversity receiving system comprising a pair of receiving channels, a first signal combining circuit comprising a pair of electron discharge devices having a push-pull output -circuit, a second signal combining circuit comprising a pair of electron discharge devices having a push-push output circuit, connections from one of said receiving channels-to the control electrodes of only one device of each of said first and second signal combining circuits, connections irom the other receiving channel to the control electrodes of the other devices of each of said first and second signal combining circuits, a rectifier coupled to the output of said first signal combining circuit, a rectifier coupled to the output of said second signal combining circuit, a direct connection between the cathodes of said rectifiers,`an alternating current circuit coupled to said cathodes, and an angular velocity detection circuit coupled to said alternating current circuit, and a common bias resistor for said two rectifiers so arranged that the strongest signal passing through one combining circuit and rectified by its associated rectiiier produces a negative bias on said resistor to reduce the useful output from the other combining circuit, a

condenser shunting said common bias resistor, and a connection to the high potential side of said resistor for deriving detected modulation output from said system.

5. A diversity receiving system comprising a pair of receiving channels each of which has individual thereto an antenna and a frequency converter for producing an intermediate frequency output from the channel, iirst and second signal combining circuits each having a pair of vacuum tubes, said tubes each including a cathode, a control grid and an ranode, a direct connection between the cathodes of each combining circuit, a parallel tuned output circuit for said first combining circuit, connections from the anodes of the tubes of said rst combining circuit to opposite terminals of said parallel tuned circuit to thereby produce a push-pull output, a direct connection between the anodes of the tubes of said second combining circuit, a parallel tuned output circuit for said second combining circuit, said last tuned circuit having one terminal connected to the anodes of said last tubes to thereby produce a push-push output for said second combining circuit, connections from the same intermediate frequency output terminal of one receiving channel to the control grids of only one tube of each of said combining circuits, connections from the same intermediate lfrequency terminal of the other receiving channel to the control grids of the other tubes of said combining circuits, a connection from the other intermediate frequency output terminal of said one receiving channel to the cathodes of one of said combining circuits, :a connection from the other intermediate frequency output terminal of said other receiving .channel to the cathodes of said other combining circuit, each of said last connections including a grid leak-shunt condenser arrangement, and a common output for said two signal combining circuits.

6. A diversity receiving system comprising a pair of receiving channels each of which has individual thereto an antenna and a frequency converter for producing an intermediate frequency output from the channel, rst and second signal combining circuits each having a pair of vacuum tubes, said tubes each including a cathode, a control grid and an anode, a direct connection between the cathodes of each combining circuit, a parallel tuned output circuit for said iirst combining circuit, connections from the anodes of the tubes of said irst combining ,circuit to opposite terminals of said parallel tuned circuit to thereby produce a push-pull output, aA direct connection between the anodes of the tubes of said second combining circuit, a parallel tuned output circuit for said second combining circuit, said last tuned circuit having one terminal connected to the' anodes of said last tubes to thereby produce a push-push output for said second combining circuit, connections from the same intermediate frequency output terminal of one receiving channel to the control grids of only one tube of each of said combining circuits, connections from the same intermediate frequency terminal of the other receiving channel to the control grids of the other tubes of said combining circuits, a connection from the other intermediate frequency output terminal of said one receiving channel to the cathodes of one of said combining circuits, a connection from the other intermediate Vfrequency output terminal of said other receiving channel to the cathodes ci said otherfcombining circuit,

each of said last connectionsincludingagrid leak-shunt condenser arangmentyla rectifier coupled to the output, of s'aid liii-'st 14sig ombining circuit, a rectifier coupled`ft`o^fthe"output of said second signal combining `ci'i'i`cui'l'`'aiidifa common bias resistor for .said two e'ct'iiieis so arranged that the strongest 1sigrial `=p`ass`i"ng through one combinin'ghcircuit and recti'fi'dfby its associated rectier'produces janegativebias on said'res'istor to reduce `the useful output from the other combining circuit, and a common utilization circuit coupled to both rectiiiers.

7. A diversity receiving systemhaving two receiving channels, individual radio :frequency pick-ups coupled to skid channels, a rst signal combining circuit arrangedy to eect an in-phase combination, a second signal combining circuit arranged to s; effect ari out-Tof'- phase combination, means for iimpressing the same signal from both channels on both combining circuits, said means including connections from each channel to different input terminals of both signal combining circuits, circuits coupling together the outputs of both signal combining circuits in such manner and being so constructed and arranged that the predominant use- `ful signal from one combining circuit reduces the signal from the other combining circuit, and a utilization circuit coupled in common to the outputs of both signal combining circuits.

8. A diversity receiving system having two receiving channels, a first signal combining circuit arranged to eec't an in-phase combination, a second signal combining circuit arranged to effect an out-of-phase combination, connections from both channels to different input terminals of both signal combining circuits, a rectifier coupled to the output of said first signal combining circuit, a rectifier coupled to the output of said second signal combining circuit, and a common bias resistor for said two rectiers so arranged that the strongest signal passing through one combining circuit and rectied by its associated rectier produces a negative bias on said resistor to reduce the useful output from the other combining circuit, and a useful load circuit coupled to both rectifiers.

il. The method of operating a diversity receiving system which comprises collecting signal energy at a pair of spaced points, causing the signals collected :at said two points to additively combine in one path when they are out-ofphase by 180 and to oppose each other in another path at this same phase relation, causing the signals collected at said two points to oppose in said one path and to additively combine in the other path when they are in-phase, and utilizing the resultant energies.

10. The method of operating a diversity receiving system which comprises collecting signal energy at a pair of spaced points, causing the signals collected at said two points to additively combine in one path when they are out-of-phase by 180 and to oppose each other in another path at this same phase relation, causing the signals collected at said two points to oppose in said one path and to addltively combine in the other path when they are in-phase, and utilizing the predominant output from one of said paths at other phase relations between collected signals to reduce the contribution from the other of said paths.

1l. A diversity receiving system comprising a pair of receiving channels, a first signal combining circuit comprising a pair of electron disniet@ einige devicesnavmg" a fpusicpii output ci' it, a second signal combining circuit comprising "a pair of electron vdischai-gfeldevices having apush p'lish output" circuit; connections vfrom one of said receiving channelslfto the'control electrodes of only one device of' each of 'sai'd'firstand second signal `confiliining circuits, vconriections Jfrom `the other receiving :channel to the control electrodes of tliei other Alldevices v yof each of saidl :first and second signal combining-f' circuits, third and fourth pairs o coiriblningI circuitssimilarlyf constru'c't'ed tofsai'd yfirstfand-lsecond combining circu'i'ts'f andv similaiily`f cbupl`ejd to said Vreceii/i'ng channels, far 'phase shifterbetweeri "oi'iiof said receiving channels anldsaicl third and fourth combining circuits, andn al common utilization circuit winne@v to :the outputs crauof" said combining circuits.y I i F a 12. Aidiversity receiving system comprising" la pair of receiving channels, a iirst signal combining circuit comprising a pair of electron discharge devices having a push-pull output circuit, a second signal combining circuit comprising a pair of electron discharge devices having a pushpush output circuit, connections from one of said receiving channels to the control electrodes of only one device of each of said first and second signal combining circuits, connections from the other receiving channel to the control electrodes of the other devices of each of said rst and second signal combining circuits, third and fourth pairs of combining circuits similarly constructed to said first and second combining circuits and similarly coupled to said receiving channels, a 90 phase shifter between one of said receiving channels and said third and fourth combining circuits, individual rectiers for rectifying the outputs of said first, second, third and fourth combining circuits, a common bias resistor for all of said rectii'lers so arranged that the predominant signals in the outputs 'of said combining circuits will reduce the contributions from the other combining circuits at all phase relations.

13. A diversity receiving system having two receiving channels, a first signal combining circuit arranged to effect an in-phase combination, a second signal combining circuit arranged to effect an out-of-phase combination, connections from both channels to different input terminals of both signal combining circuits, third and fourth signal combining circuits which are respectively similar to said first and second signal combining circuits and similarly connected to both said receiving channels, a 90 phase shifter located between said channels and said third and fourth combining circuits, means for rectifying the output of each combining circuit, a common bias resistor for said means, and a common load circuit coupled to said rectifiers.

14. A diversity receiving system having two receiving channels, a first signal combining circuit having a push-pull input and a push-pull output, a Second signal combining circuit having Ia push-pull input and a push-push output, connections from both channels to different input terminals of both signal combining circuits, third and fourth signal combining circuits which are respectively similar to said rst and second signal combining circuits and similarly connected to both said receiving channels, a 90 phase shifter located between said channels and said third and fourth combining circuits, means for rectifying the output of each combining circuit, a common bias resistor for said means, and means Vfor deriving -either or both alternating current 11 output and detected modulation output from said rectiflers.

15. A diversity receiving system comprising a pair of receiving channels, a first signal combining circuit comprising a pair of electron discharge devices having a push-pull output circuit,4 a second signal combining circuit comprising a pair of electron discharge devices having a a push-push output circuit, connections from one of said receiving channels to the control electrodes of only one device of each of said first and second signal combining circuits, connections from the other receiving channel to the control electrodes of the other devices of each of said first and second signal combining circuits, a rectifier coupled to the output of said first signal combining circuit, a rectiiler coupled to the output of said second signal combining circuit,` a connection between the cathodes of 12 said rectitlers. an alternating current circuit 4coupled to said cathodes, and an angular velocity detection circuit coupled to saidfalternating current circuit, and a common bias resistor for said two rectiilers so arranged that the strongest signal passing through one combining circuit and rectified by its associated rectifier produces a negative bias on said resistor to reduce the useful output from the other combining circuit.

MURRAY G. CROSBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,719,845 Martin July 9, 1929' 2,350,702 Ullrich June 6, 1941 

